Thermal diffuser and cooling apparatus for cooling heat source using the same

ABSTRACT

A thermal diffuser includes a plurality of thermally-conductive plates, each of which has a strip-like shape. The plurality of thermally-conductive plates is laminated onto one another in a plate-thickness direction of the strip-like shape to form a laminated body. Each of the plurality of thermally-conductive plates has thermal conductivities in a longitudinal direction and in a width direction of the strip-like shape better than a thermal conductivity in the plate-thickness direction. The thermally-conductive plates has sides, each of which extends in the longitudinal direction. The laminated body is formed such that the sides of the thermally-conductive plates form a plate surface of the laminated body, which surface extends in the plate-thickness direction that serves as a lamination direction, in which the thermally-conductive plates of the laminated body are laminated. A direction perpendicular to the plate surface corresponds to a thickness direction of the laminated body.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2010-132076 filed on Jun. 9, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal diffuser that transfers heat of a heat source, such as a semiconductor device, and relates to a cooling apparatus that uses the thermal diffuser to cool the heat source.

2. Description of Related Art

JP-A-2005-272164 shows a conventional thermal diffuser (high thermal conductivity member) for cooling a heat source. The conventional thermal diffuser employs, for example, a graphite structure to replace a metal material, such as copper and aluminum. A single graphite structure (or a graphene) has an a-b axial direction, which extends in a plane direction of the graphene. The thermal conductivity of the graphite structure in the a-b axial direction exceeds 1000 W/mK, and is twice or more of the thermal conductivity (350 to 400 W/mK) of copper and is four times or more of the thermal conductivity (200 to 250 W/mK) of aluminum. However, the single graphite structure has a thermal conductivity in the layer direction (or the thickness direction), which is equal to or less than 10 W/mK. In order to improve the thermal conductivity in the layer direction, JP-A-2005-272164 proposes a certain graphite structure, which has the a-b axis oriented in the direction (plane direction) parallel to a plate surface, and which has a carbon structure therein.

Thus, while the high thermal conductivity in the plane direction of the graphite structure, which serves as a mother body, is maintained, it is possible to efficiently transmit the heat in the layer direction through the carbon structure due to the carbon structure, which is made of carbon fiber polymer, and which is provided within the graphite structure as required. As a result, compared with the single graphite structure, it is possible to improve the thermal conductivity in the layer direction, and also it is possible to increase the tensile strength and the thickness of the thermal conductivity member.

However, in the description (paragraphs 0077, 0083, 0086, 0093) in JP-A-2005-272164, the thermal conductivity in the layer direction is about 20 to 100 W/mK even after the thermal conductivity has been improved. Thus, the improved thermal conductivity in the layer direction is still several times to ten times of the thermal conductivity (10 W/mK) of the single graphite structure in the layer direction. As a result, the improved thermal conductivity is still very low compared with the thermal conductivity of the metal material, such as copper or aluminum.

SUMMARY OF THE INVENTION

The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages.

To achieve the objective of the present invention, there is provided a thermal diffuser that includes a plurality of thermally-conductive plates, each of which has a strip-like shape. The plurality of thermally-conductive plates is laminated onto one another in a plate-thickness direction of the strip-like shape to form a laminated body. Each of the plurality of thermally-conductive plates has thermal conductivities in a longitudinal direction and in a width direction of the strip-like shape better than a thermal conductivity in the plate-thickness direction. The thermally-conductive plates have sides, each of which extends in the longitudinal direction. The laminated body is formed such that the sides of the thermally-conductive plates form a plate surface of the laminated body, which surface extends in the plate-thickness direction that serves as a lamination direction, in which the thermally-conductive plates of the laminated body are laminated. A direction perpendicular to the plate surface corresponds to a thickness direction of the laminated body.

To achieve the objective of the present invention, there is also provided a cooling apparatus for a heat source, the cooling apparatus including the thermal diffuser, a heat source, an insulating plate, and a cooling unit. The plate surface of the thermal diffuser is one of a plurality of plate surfaces. The heat source is provided to one of the plurality of plate surfaces of the thermal diffuser. The insulating plate is provided to the other one of the plurality of plate surfaces of the thermal diffuser. The cooling unit is provided to a surface of the insulating plate opposite from the thermal diffuser.

To achieve the objective of the present invention, there is also provided a cooling apparatus for a heat source, the cooling apparatus including the thermal diffuser, a heat source, and an insulating plate. The thermal diffuser includes two laminated bodies. The plate surface of the thermal diffuser is one of a plurality of plate surfaces. The heat source is provided to one of the plurality of plate surfaces of the thermal diffuser. The insulating plate is provided to the other one of the plurality of plate surfaces of the thermal diffuser. The cooling unit is provided to a surface of the insulating plate remote from the thermal diffuser. One of the two laminated bodies of the thermal diffuser has a thickness dimension of t1. The other one of the two laminated bodies has a thickness dimension of t2. A distance, which is measured from a center position of the heat source to an end of the thermal diffuser in a longitudinal direction of the thermally-conductive plates of the one of the laminated bodies, is defined as r1. A distance, which is measured from the center position of the heat source to another end of the thermal diffuser in the longitudinal direction of the thermally-conductive plates of the other one of the laminated bodies, is defined as r2. The dimensions t1, t2, and the distances r1, r2 satisfy the equation of 0.5≦(t1/t2)/(r1/r2)≦2.

To achieve the objective of the present invention, there is also provided a method of manufacturing a thermal diffuser. In the method, a laminated body is formed by laminating a plurality of thermally-conductive plates, each of which has a plate shape, in a plate-thickness direction of the plate shape. Each of the plurality of thermally-conductive plates has a thermal conductivity in a plane direction of the plate shape better than a thermal conductivity in the plate-thickness direction. A plate member is formed by cutting the laminated body in a lamination direction, in which the thermally-conductive plates are laminated, along one sides of the thermally-conductive plates such that the plate member has a plate shape. The plate member is formed such that one sides of the thermally-conductive plate form a plate surface that extends in the lamination direction. A direction perpendicular to the plate surface corresponds to a thickness direction of the plate member.

To achieve the objective of the present invention, there is also provided a method for manufacturing a thermal diffuser. In the method, a laminated body is formed by laminating a plurality of thermally-conductive plates, each of which has a plate shape, in a plate-thickness direction of the plate shape. Each of the plurality of thermally-conductive plates has a thermal conductivity in a plane direction of the plate shape better than a thermal conductivity in the plate-thickness direction. A primary plate member is formed by cutting the laminated body in the lamination direction along one sides of the thermally-conductive plates such that the primary plate member has a plate shape. The primary plate member is formed such that the one sides of the thermally-conductive plates form a plate surface that extends in a lamination direction, in which the plurality of thermally-conductive plates is laminated. A direction perpendicular to the plate surface corresponds to a thickness direction of the primary plate member. A secondary plate member is formed by cutting off four corners of the primary plate member such that the secondary plate member has a rectangular shape, wherein a direction, in which the one sides of the thermally-conductive plates extend, is angled relative to each side of the secondary plate member. The forming of the secondary plate member includes forming a plurality of secondary plate members. The plurality of secondary plate members is arranged in a direction, in which the plate surface extends. A part of the plate surface of each of the plurality of secondary plate members is included in a connecting region that is connected with a heat source. Each of the plurality of secondary plate members has an outer peripheral section that forms an outer periphery of an entirety of the plurality of secondary plate members. Any point within the connecting region and any point on the outer peripheral section of each of the plurality of secondary plate members define an imaginary line therebetween. A direction of the one sides of the thermally-conductive plates of each of the plurality of secondary plate members is parallel to the imaginary line.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is an exploded perspective view illustrating a cooling apparatus for cooling a heat source according to the first embodiment of the present invention;

FIGS. 2A and 2B are perspective views each illustrating a thermal diffuser in FIG. 1;

FIGS. 3A to 3D are perspective views illustrating a method for manufacturing a thermal diffuser according to the second embodiment of the present invention;

FIG. 4 is an exploded perspective view illustrating a cooling apparatus for cooling a heat source according to the third embodiment of the present invention;

FIGS. 5A and 5B are perspective views illustrating a method for manufacturing a thermal diffuser in FIG. 4;

FIG. 6 is a chart illustrating the thermal conductivity in the thickness direction of the thermal diffuser shown in FIG. 4;

FIG. 7 is a perspective view illustrating a cooling apparatus for cooling a heat source according to the fourth embodiment of the invention;

FIG. 8 is a perspective view illustrating a cooling apparatus for cooling a heat source according to the fifth embodiment of the present invention;

FIG. 9 is a perspective view illustrating a cooling apparatus for cooling a heat source according to the sixth embodiment of the present invention;

FIG. 10 is an exploded perspective view illustrating a cooling apparatus for cooling a heat source according to the seventh embodiment of the present invitation;

FIG. 11 is a perspective view illustrating the thermal diffuser shown in FIG. 10; and

FIGS. 12A to 12D are perspective views illustrating a method for manufacturing the thermal diffuser shown in FIG. 10.

DETAILED DESCRIPTION OF EMBODIMENTS

Several embodiments of the present invention will be described below with reference to accompanying drawings. Components, which have been already described in the preceding embodiment, are indicated by the same numeral used in the preceding embodiment, and the redundant description thereof may be omitted. When only a part of the configuration of the embodiment is described, the other part of the configuration may employ the description of the preceding embodiment. Any combination of parts of the embodiments is possible even though the above combination is not explicitly described in the embodiments provided that the combination does not cause any significant deficiency.

First Embodiment

A cooling apparatus 100A for cooling a heat source in the first embodiment will be described blow with reference to FIG. 1 and FIGS. 2A and 2B. FIG. 1 is an exploded perspective view illustrating the cooling apparatus 100A of the heat source, and FIGS. 2A and 2B are perspective views each illustrating a thermal diffuser 110 made of thermal conductivity plates in FIG. 1.

As shown in FIG. 1, the cooling apparatus 100A for cooling the heat source (hereinafter, simply referred to as the cooling apparatus 100A) includes the thermal diffuser 110, a heat source 120, an insulating plate 130, and a cooling unit 140. The cooling apparatus 100A cools the heat source 120 by transmitting heat of the heat source 120 to the cooling unit 140 through the thermal diffuser 110.

As shown in FIG. 2, the thermal diffuser 110 is a plate that efficiently transmits heat of the heat source 120 toward the cooling unit 140, and the thermal diffuser 110 includes multiple thermally-conductive plates 111. Each of the thermally-conductive plates 111 is a very thin plate member having a strip-like shape. The thermally-conductive plate 111 has thermal conductivities in a longitudinal direction and in a width direction better than a thermal conductivity in a plate-thickness direction. The thermally-conductive plate 111 is made of, for example, a graphite material, or alternatively of a composite material, which has graphite and metal. The metal of the above composite material employs, for example, copper and aluminum. Specifically, as above, the graphite material has great thermal conductivities in a plate-thickness direction and in a width direction of the thermally-conductive plate 111. In other words, the graphite material is a highly oriented graphite material having great thermal conductivities in two directions that extend along a plate surface (or a top surface) of the graphite material.

The thermally-conductive plates 111 are laminated onto one another in the plate-thickness direction to form a plate-shaped laminated body. In the first embodiment, the laminated body serves as the thermal diffuser 110. In other words, in the laminated body, the thermally-conductive plate 111 has a long side 111 a that extends in a longitudinal direction, and the long sides 111 a forms a plate surface 110 a having a plate shape that extends in a lamination direction, in which the thermally-conductive plates 111 are laminated (see FIG. 2B). Furthermore, a direction orthogonal to the plate surface 110 a corresponds to a thickness direction of the laminated body having the plate shape. The thermal diffuser 110 has a plate shape that has a dimension in the lamination direction greater than a dimension of the thermally-conductive plate 111 in the width direction. The plate surface 110 a is, in other words, a plane defined by (a) the long side 111 a and (b) a side that extends in the lamination direction. The thermal diffuser 110 has a dimension in the thickness direction, which dimension is equivalent to a dimension of the thermally-conductive plate 111 in the width direction. As a result, the thermal diffuser 110 has better thermal conductivities in two directions (see FIGS. 2A and 2B in this regard). More specifically, the two directions include the direction of the long side 111 a of the plate surface 110 a, and the thickness direction of the plate-shaped laminated body.

It is noted that the thermal diffuser 110 is formed as the laminated body by laminating the multiple thermally-conductive plates 111 onto one another, and then by baking the thermally-conductive plates 111. Alternatively, a gaseous material, such as a highly oriented graphite material, or a composite material having a highly oriented graphite and metal, is sequentially sprayed on a plane to form the laminated body.

The heat source 120 is a semiconductor device, for example, an IGBT (insulated gate bipolar transistor) or an FWD (flywheel diode), which generates heat when operated. For example, the thermal diffuser 110 includes two plate surfaces 110 a (top and bottom plate surfaces 110 a). There are multiple heat sources 120 (two generators 120 in the present embodiment), and the heat sources 120 are provided to contact one of the plate surfaces 110 a of the thermal diffuser 110.

The insulating plate 130 is a plate member made of a ceramics for electrically insulating the heat source 120, for example. The insulating plate 130 is provided to contact the other one of the plate surfaces 110 a of the thermal diffuser 110 opposite from the one plate surface 110 a, to which the heat source 120 is provided.

The cooling unit 140 is a heat exchanger that cools the heat source 120 by transferring heat of the heat source 120 to a cooling medium that flows through the internal passages 142. The cooling unit 140 is provided to contact a surface of the thermal diffuser 110 opposite from the insulating plate 130. The cooling unit 140 includes a main body part 141 having a plate shape and defining therein the main passages 142. The passages 142 are formed to admit cooling medium (for example, cooling air, coolant) to flow therethrough.

In the above cooling apparatus 100A, heat of the heat source 120 spreads along the plate surface 110 a of the thermal diffuser 110 (or spreads in the direction of the long side 111 a) to an outer periphery, and also is transferred in the thickness direction of the thermal diffuser 110. Furthermore, the heat is transferred in a plate-thickness direction of the insulating plate 130 to reach the main body part 141 of the cooling unit 140. In the cooling unit 140, the above transferred heat of the heat source 120 is given to the cooling medium flowing through the internal passages 142, and thereby the heat source 120 is successfully cooled.

In the present embodiment, the thermally-conductive plate 111 of the thermal diffuser 110 has better thermal conductivities in the longitudinal direction and in the width direction than a thermal conductivity in the plate-thickness direction. The thermal diffuser 110 is made by laminating the thermally-conductive plates 111 in the plate-thickness direction. In the above, the plate surface 110 a is formed by the longitudinal sides 111 a of the thermally-conductive plates 111 and extends in the lamination direction. Because of the above formed plate surface 110 a, it is possible to provide a better thermal conductivity in the longitudinal direction of the thermally-conductive plate 111. Also, in the above configuration, the thickness direction, which is orthogonal to the plate surface 110 a of the thermal diffuser 110, coincides with the width direction of the thermally-conductive plate 111 as shown in FIG. 2B. As a result, it is possible to provide a better thermal conductivity in the thickness direction of the thermal diffuser 110. Thereby, the thermal diffuser 110 has better thermal conductivities in two directions (see the highly thermal conductive directions shown in FIGS. 1, 2A and 2B). More specifically; one of the two directions, in which the thermal conductivities act better, is a direction parallel to the plate surface 110 a of the thermal diffuser 110 and perpendicular to the lamination direction. The other of the two directions is the thickness direction (or a layer direction) of the thermal diffuser 110. As a result, it is possible to efficiently transfer the heat of the heat source 120 to the cooling unit 140.

Second Embodiment

FIGS. 3A to 3D show a thermal diffuser 110 of the second embodiment, and more specifically show a manufacturing process of the thermal diffuser 110. The method of manufacturing the thermal diffuser 110 in the second embodiment is different from the manufacturing method in the first embodiment (FIG. 1, FIG. 2).

The method for manufacturing the thermal diffuser 110 will be described below. Firstly, the plate-shaped thermally-conductive plates 111 having a better thermal conductivity in the plane direction than the thermal conductivity in the plate-thickness direction are prepared (FIG. 3A). The thermally-conductive plates 111 are laminated on one another in the plate-thickness direction to form a laminated body (FIG. 3B).

Next, the laminated body formed as above is cut in the lamination direction along the one side 111 b of the thermally-conductive plate 111 to form a plate member as shown in FIG. 3C. Then, in the plate member, the plate surface 110 a of the thermal diffuser 110 is defined by a surface made by the lamination of the one sides 111 b of the thermally-conductive plates 111 in the lamination direction. Also, the thickness direction of the thermal diffuser 110 is defined to be orthogonal to the plate surface 110 a (FIG. 3D).

As a result, the thermal diffuser 110, which is equivalent to the thermal diffuser 110 described in the first embodiment, is easily formed.

Third Embodiment

FIGS. 4 to 6 show a cooling apparatus 100B of the third embodiment. In contrast to the first embodiment (FIGS. 1 and 2), the thermal diffuser 110 of the third embodiment is made of multiple thermal diffusers 110A, 110B.

As shown in FIGS. 4, 5A, and 5B, the thermal diffuser 110 is made of two thermal diffusers (or two laminated bodies). More specifically, the thermal diffuser 110 includes a first thermal diffuser 110A and a second thermal diffuser 1108. Each of the thermal diffusers 110A, 110B is similar to the thermal diffuser 110 described in the first embodiment. The thermal diffuser 110A is arranged such that the lamination direction of the thermally-conductive plates 111 of the thermal diffuser 110A is different from the lamination direction of the thermally-conductive plates 111 of the thermal diffuser 110B. Thus, the adjacent thermal diffusers (laminated bodies) 110A, 110B have the respective lamination directions of the thermally-conductive plates 111 different from each other.

In other words, in the first thermal diffuser 110A, the lamination direction, in which the thermally-conductive plates 111 are laminated, corresponds to a depth direction in FIG. 5A. Thereby, the first thermal diffuser 110A has better thermal conductivities in a left-right direction of the plate surface 110 a in FIG. 5A (or the longitudinal direction of the thermally-conductive plate 111) and in the thickness direction of the first thermal diffuser 110A.

In contrast, in the second thermal diffuser 110B, a lamination direction, in which the thermally-conductive plates 111 are laminated, corresponds to the left-right direction in FIG. 5A. As a result, the second thermal diffuser 110B has better thermal conductivities in the depth direction of the plate surface 110 a in FIG. 5A (or in the longitudinal direction of the thermally-conductive plate 111) and in the thickness direction of the second thermal diffuser 110B.

The first thermal diffuser 110A and the second thermal diffuser 110B are laminated in the thickness direction, and an inorganic bonding layer (inorganic layer) 112 interposed between the thermal diffusers 110A, 110B bonds the thermal diffusers 110A, 110B each other. The bonding layer 112 includes at least one of titanium (Ti), nickel (Ni), tin (Sn), lead (Pb), and gold (Au). In the present embodiment, the bonding layer 112 is solder having tin (Sn). Solder has a thermal conductivity of 60 W/mK.

The thermal diffuser 110 formed as above includes the first thermal diffuser 110A and the second thermal diffuser 110B, and the lamination direction of the thermally-conductive plates 111 of the first thermal diffuser 110A is different from the lamination direction of the thermally-conductive plates 111 of the second thermal diffuser 110B. More specifically, the above lamination directions intersect with each other. Specifically, the lamination directions intersect at a right angle (or at the angle of 90 degrees). The angle defined by the lamination directions may be in a range from 85 to 90 degrees in order to enhance the thermal conductivities in the two axial directions along the plate surface 110 a.

In the thermal diffuser 110 of the present embodiment, the plate surface 110 a of the first thermal diffuser 110A has a first direction, in which the thermal conductivity of the first thermal diffuser 110A acts better, and the plate surface 110 a of the second thermal diffuser 1108 has a second direction, in which the thermal conductivity of the second thermal diffuser 110B acts better. In the thermal diffuser 110 of the present embodiment, the first direction and the second direction define therebetween the angle in a range from 85 to 90 degrees. As a result, when observed as the entirety of the thermal diffuser 110, which has the thermal diffusers 110A, 110B laminated in thickness direction, it is possible to cause the thermal diffuser 110 to have better thermal conductivities in the thickness direction and also in the two directions, which are orthogonal to each other, along the plate surface 110 a. Thus, it is possible to provide the thermal diffuser 110 that has thermal conductivities that acts better in three axial directions, and thereby it is possible to efficiently cool the heat source 120.

FIG. 6 is a chart illustrating a thermal conductivity in the thickness direction of the thermal diffuser 110 made of the multiple thermal diffusers 110A, 1108 as a function of the thermal conductivity of the bonding layer 112. In one model of the present embodiment, each of the thermal diffusers 110A, 1108 has a length of 32 mm, a width of 18 mm, and a thickness of 1 mm. The bonding layer 112 has a thickness of 0.1 mm. In the above dimension, the thermal conductivity in the thickness direction of the thermal diffuser 110 is studied. When the bonding layer 112 (or solder) has the thermal conductivity of 60 W/mK, the thermal conductivity in the thickness direction of the thermal diffuser 110 indicates 600 W/mK. The above value is much higher than the thermal conductivity of copper or aluminum.

In the embodiment, the thermal diffuser 110 includes two thermal diffusers 110A, 110B. However, the thermal diffuser 110 may alternatively include three or more thermal diffusers that are laminated. In the above alternative case, the adjacent thermal diffusers among the three or more thermal diffusers may be arranged such that the direction, in which one thermal diffuser has a better thermal conductivity, is set different from the direction, in which the adjacent thermal diffuser has a better thermal conductivity. More specifically, the above directions of the adjacent thermal diffusers may define the angle in a range from 85 to 90 degrees.

Fourth Embodiment

FIG. 7 shows a cooling apparatus 100C according to the fourth embodiment. In the fourth embodiment, a metal plate 150 is added to the structure of the third embodiment (FIG. 4).

The metal plate 150 is a highly conductive plate made of, for example, copper or aluminum, and is provided between the thermal diffuser 110 and the insulating plate 130.

In the present embodiment, the insulating plate 130 prevents electric leakage toward the cooling unit 140, and the metal plate 150 is employed as an electric power output terminal of the heat source (semiconductor device) 120.

Fifth Embodiment

FIG. 8 shows a cooling apparatus 100D according to the fifth embodiment of the present invention. In the fifth embodiment, a position of the metal plate 150 is changed from a position in the fourth embodiment (FIG. 7).

In the fourth embodiment (FIG. 7), the metal plate 150 is provided between the thermal diffuser 110 and the insulating plate 130. However, in the present embodiment (FIG. 8), the metal plate 150 is alternatively provided between the heat source 120 and the thermal diffuser 110.

In the present embodiment, it is possible to bring the heat source (semiconductor device) 120 into direct contact with the metal plate 150. As a result, in a case, where the heat source 120 is used with a large electric current, it is possible to more effectively limit the influence of the electrical resistance of the thermal diffuser 110 compared with the fourth embodiment (FIG. 7). Therefore, it is possible to effectively employ the metal plate 150 as the electric power output terminal of the heat source 120.

Sixth Embodiment

FIG. 9 shows a cooling apparatus 100E according to the sixth embodiment of the present invention. The sixth embodiment is a modification of the third embodiment (FIG. 4). In the present embodiment, a dimension of the thermal diffuser 110 in the thickness direction is effectively defined in consideration of the position of the heat source 120 relative to the thermal diffuser 110.

The first thermal diffuser 110A of the thermal diffuser 110 serves as one of the two laminated bodies that constitute the thermal diffuser 110. In the first thermal diffuser 110A, the longitudinal direction of the thermally-conductive plate 111 coincides with a left-right direction in FIG. 9. In other words, a direction (highly thermally conductive direction), which the thermal conductivity of the plate surface 110 a of the first thermal diffuser 110A acts better corresponds to the left-right direction in FIG. 9. In addition to the above, the thermal conductivity of the plate surface 110 a of the first thermal diffuser 110A acts better in the thickness direction of the first thermal diffuser 110A. Also, the second thermal diffuser 1108 of the thermal diffuser 110 serves as the other one of the laminated bodies that constitute the thermal diffuser 110. In the second thermal diffuser 110B, the longitudinal direction of the thermally-conductive plate 111 coincides with the depth direction in FIG. 9. In other words, a direction, in which the thermal conductivity of the plate surface 110 a of the second thermal diffuser 110B acts better, coincides with the depth direction in FIG. 9. In addition to the above, the thermal conductivity of the plate surface 110 a of the second thermal diffuser 110B acts better in the thickness direction of the second thermal diffuser 110B. Also, the first thermal diffuser 110A has a dimension of t1 in the thickness direction, and the second thermal diffuser 110B has a dimension of t2 in the thickness direction.

The single heat source 120 is provided to the plate surface 110 a of the thermal diffuser 110 (or the first thermal diffuser 110A). The heat source 120 has a center position a when observed from the upper side in FIG. 9 (or observed in a direction orthogonal to the plate surface 110 a). In the plate surface 110 a of the first thermal diffuser 110A, a longer distance measured in the highly thermally conductive direction (left-right direction) of the first thermal diffuser 110A from the center position a to an end portion of the first thermal diffuser 110A is defined as r1. Also, in the plate surface 110 a of the first thermal diffuser 110A, a longer distance measured in the highly thermally conductive direction (depth direction) of the second thermal diffuser 110B from the center position a to an end portion of the first thermal diffuser 110A is defined as r2.

In the present embodiment, the dimensions t1, t2 in the thickness direction and the distances r1, r2 satisfy the following relation shown by equation 1.

0.5≦(t1/t2)/(r1/r2)≦2  (equation 1)

In the present embodiment, in the first thermal diffuser 110A, when the distance r1 is greater, it is better to transfer the heat of the heat source 120 in the direction toward the end, to which the distance r1 is measured. Similarly, in the second thermal diffuser 110B, when the distance r2 is greater, it is better to transfer the heat of the heat source 120 in the direction toward the end, to which the distance r2 is measured. Then, the dimension of each of the thermal diffusers 110A, 110B in the thickness direction is changed to larger or smaller depending on the heat to be transferred. In other words, when the distance r1 (r2) is large, it is possible to increase the dimension t1 (t2). In contrast, when the distance r1 (r2) is small, it is necessary to decrease the dimension t1 (t2). As a result, in order to achieve the good thermal conductivity of the thermal diffuser 110, theoretically, the ratio of r1 to r2 is made coincide with the ratio of t1 to t2. In other words, a value of (r1/r2) is made equivalent to a value of (t1/t2), and thereby an equation of (t1/t2)/(r1/r2)=1 is satisfied. In practice, the value of (t1/t2)/(r1/r2) is set in a range from 0.5 to 2.0 around the above theoretical value of 1, and thereby it is possible to achieve the good thermal conductivity of the thermal diffuser 110. As a result, it is possible to effectively cool the heat source 120.

In the present embodiment, the metal plate 150 may be provided similarly to the fourth embodiment (FIG. 7), or to the fifth embodiment (FIG. 8).

Seventh Embodiment

FIGS. 10 to 12D show a cooling apparatus 100F according to the seventh embodiment of the present invention. In the seventh embodiment, in contrast to the first and second embodiments (FIG. 1 to FIG. 3D), the thermal diffuser 110 includes thermal diffusers 110C to 110F, and the thermal diffuser 110 is provided between the insulating plate 130 and the metal plate 150, which is described in the fourth embodiment (FIG. 7). Also, the single heat source 120 is provided to the plate surface 110 a of the thermal diffuser 110.

As shown in FIG. 10, the thermal diffuser 110 is made of the four thermal diffusers 110C to 110F in the present embodiment. Each of the thermal diffusers 110C to 110F is a laminated body made by laminating the multiple thermally-conductive plates 111, and has the plate surface 110 a that forms a rectangular plate shape. Each of the thermal diffusers 110C to 110F is provided such that the respective plate surface 110 a of each of the thermal diffusers 110C to 110F is flush with each other. Also, simultaneously, the thermal diffusers 110C to 110F respectively have one corner portions that are located at a certain position such that adjacent sides of the thermal diffusers 110C to 110F are in contact with each other.

Because a part (corner portion) of each of the thermal diffusers 110C to 110F is located around the certain position, an area around the certain position serves as a connecting region that is connected with the heat source 120. The connecting region is connected with the heat source 120, and the heat source 120 is connected with the part (corner portion) of each of the thermal diffusers 110C to 110F.

FIG. 11 shows the thermal diffuser 110C as a representative of the thermal diffusers 110C to 110F. As shown in FIG. 11, each of the thermal diffusers 110C to 110F has the longitudinal direction of the thermally-conductive plates 111 (or the direction of the one sides 111 b), which is different from each other in contrast to the thermal diffuser 110 of the first and second embodiments (FIG. 1 to FIG. 3D). Hereinafter, “the longitudinal direction of the thermally-conductive plates 111, or the direction of the one sides 111 b” is referred to as “the direction of the one side 111 b of the thermally-conductive plate 111” as shown in FIGS. 12A to 12D. For example, the direction of the one side 111 b of the thermally-conductive plate 111 of the thermal diffuser 110C is different from the direction of the one side 111 b of the thermally-conductive plate 111 of the thermal diffuser 110D.

For example, each of the thermal diffusers 110C to 110F has four sides L1, L2, L3, L4 that define an outer periphery of the rectangular shape thereof as shown in FIG. 11. The direction of the one side 111 b of the thermally-conductive plate 111 in each of the thermal diffusers 110C to 110F is designed to be angled relative to each of the four sides L1, L2, L3, L4. More specifically, in the present embodiment, each of the thermal diffusers (or laminated bodies) 110C to 110F has a certain side (or an outer peripheral section) that forms an outer periphery of an entirety (or integral body) of the four thermal diffusers 110C to 110F. In the example of the thermal diffuser 110C of FIG. 11, the sides L1, L2 serve as the certain side. Any point (A) within the connecting region, which is connected with the heat source 120, and any point (B), which is located on the certain side (or the outer peripheral section) of each of the thermal diffusers 110C to 110F, defines an imaginary line therebetween. In the above definition, the direction of the one side 111 b of the thermally-conductive plate 111 of each of the thermal diffusers 110C to 110F is parallel to the corresponding imaginary line defined between the point (A) and the point (B).

In the present embodiment, the corner portion of each of the thermal diffusers 110C to 110F contact each other at any point (hereinafter, point A) in the connecting region. Also, the sides L1, L2 intersect at the point B, which corresponds to a corner portion defined by the sides L1 and L2. The imaginary line is equivalent to one of the diagonal lines that extend from the point A in the thermal diffusers 110C to 110F. As a result, the one side 111 b of the thermally-conductive plate 111 in the thermal diffuser 110 radially outwardly extends from the point A (see FIG. 10). Due to the above configuration, the thermal diffuser 110C and the thermal diffuser 110E, which are positioned diagonally to each other, are substantially the same. Also, the thermal diffuser 110D and the thermal diffuser 110F, which are positioned diagonally to each other, are substantially the same.

Each of the thermal diffusers 110C to 110F is manufactured in a process, for example, as shown in FIGS. 12A to 12D. In other words, similarly to the second embodiment (FIGS. 3A to 3D), the following three steps are executed in the present embodiment (FIGS. 12A to 12C). The thermally-conductive plates 111 are prepared (FIG. 12A), and subsequently the thermally-conductive plates 111 are laminated on one another in the plate-thickness direction to form the laminated body (FIG. 12B). Then, the laminated body is cut in the lamination direction along the one sides 111 b of the thermally-conductive plates 111 to form a primary plate member from the laminated body (FIG. 12C). Furthermore, four corner portions of the primary plate member are cut off, and thereby there is formed a secondary plate member having another rectangular shape inscribed in the rectangular shape of the primary plate member (FIGS. 12C and 12D). As a result, it is possible to manufacture the thermal diffusers 110C to 110F, in which the one sides 111 b of the thermally-conductive plates 111 are angled relative to each side of the secondary plate member.

Alternatively, the thermal diffuser 110 of the present embodiment may be manufactured in the following manner by using the thermally-conductive plates 111 each having the strip-like shape. For example, the thermally-conductive plates 111 are laminated in the plate-thickness direction in the ascending order of the longitudinal dimension of the thermally-conductive plates 111. Then, the thermally-conductive plates 111 are further laminated in the plate-thickness direction in the descending order of the longitudinal dimension of the thermally-conductive plates 111. As above, the plate surface 110 a, which is formed by the longitudinal sides of the thermally-conductive plates 111, and which extends in the lamination direction, is formed into the rectangular shape.

In the present embodiment, each of the thermal diffusers 110C to 110F has the one side 111 b of the thermally-conductive plate 111, which side is directed in parallel to the imaginary line extending from the point A to the point B. As a result, it is possible to cause the good thermal conductivities in the thickness direction and in the direction parallel to the imaginary line from the point A to the point B on the plate surface 110 a. Furthermore, in the thermal diffuser 110 formed by the thermal diffusers 110C to 110F, it is possible to cause the good thermal conductivities in the thickness direction and in the directions that radially outwardly extend from the point A of the thermal diffuser 110.

As a result, in the thermal diffuser 110, the heat of the heat source 120 is effectively transferred in the direction that radially outwardly extends from the heat source 120 (point A) toward the outer periphery of the thermal diffuser 110, and also, the heat of the heat source 120 is effectively transferred in the thickness direction of the thermal diffuser 110. Thereby, it is possible to effectively cool the heat source 120.

In the present embodiment, in the formation of the thermal diffuser 110, the four thermal diffusers 110C to 110F are employed. However, the present invention is not limited to the above. For example, the thermal diffuser 110 may alternatively include three thermal diffusers, or may include five or more thermal diffusers.

Also, the imaginary line between the point A to the point B on each of the thermal diffusers 110C to 110F is not limited to the diagonal line. However, the point A may be located at any position in the connecting region of the heat source 120, and the point B may be located on any position on the sides L1, L2. Thus, an imaginary line may be defined between the above alternative point A and the alternative point B. In other words, the direction of the one side 111 b of the thermally-conductive plate 111 is determined such that the direction of the one side 111 b extends from a position within the connecting region of the heat source 120 toward the outer periphery of the thermal diffuser 110.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. A thermal diffuser comprising: a plurality of thermally-conductive plates, each of which has a strip-like shape, wherein: the plurality of thermally-conductive plates is laminated onto one another in a plate-thickness direction of the strip-like shape to form a laminated body; each of the plurality of thermally-conductive plates has thermal conductivities in a longitudinal direction and in a width direction of the strip-like shape better than a thermal conductivity in the plate-thickness direction; the thermally-conductive plates has sides, each of which extends in the longitudinal direction; the laminated body is formed such that the sides of the thermally-conductive plates form a plate surface of the laminated body, which surface extends in the plate-thickness direction that serves as a lamination direction, in which the thermally-conductive plates of the laminated body are laminated; and a direction perpendicular to the plate surface corresponds to a thickness direction of the laminated body.
 2. The thermal diffuser according to claim 1, wherein the laminated body is one of a plurality of laminated bodies and the plurality of laminated bodies is laminated in the thickness direction, the thermal diffuser further comprising: an inorganic layer that is provided between the plurality of laminated bodies to bond the plurality of laminated bodies with each other; and adjacent ones of the plurality of laminated bodies have the respective lamination directions of the plurality of thermally-conductive plates different from each other.
 3. The thermal diffuser according to claim 2, wherein: the lamination directions of the plurality of thermally-conductive plates define therebetween an angle in a range from 85 to 90 degrees.
 4. The thermal diffuser according to claim 2, wherein: the inorganic layer includes at least one of titanium, nickel, tin, lead, and gold.
 5. The thermal diffuser according to claim 1, wherein: the laminated body is one of a plurality of laminated bodies that is arranged in a direction, in which the plate surface extends; a part of the plate surface of each of the plurality of laminated bodies is included in a connecting region that is connected with a heat source; each of the plurality of laminated bodies has an outer peripheral section that forms an outer periphery of an entirety of the plurality of laminated bodies; any point within the connecting region and any point on the outer peripheral section of each of the plurality of laminated bodies defines an imaginary line therebetween; and the respective longitudinal direction of the thermally-conductive plates of each of the plurality of laminated bodies is parallel to the imaginary line.
 6. The thermal diffuser according to claim 5, wherein: the plurality of laminated bodies includes four laminated bodies, the plate surface of which has a rectangular shape; and the rectangular shape of each of the laminated body has one corner portion that is included in the connecting region.
 7. The thermal diffuser according to claim 1, wherein: the laminated body has a thermal conductivity in the thickness direction equal to or greater than 600 W/mK.
 8. The thermal diffuser according to claim 1, wherein: the thermally-conductive plate is made of one of a graphite material and a composite material, which has graphite and metal.
 9. A cooling apparatus for a heat source comprising: a thermal diffuser according to claim 1, wherein the plate surface of the thermal diffuser is one of a plurality of plate surfaces; a heat source provided to one of the plurality of plate surfaces of the thermal diffuser; an insulating plate provided to the other one of the plurality of plate surfaces of the thermal diffuser; and a cooling unit provided to a surface of the insulating plate opposite from the thermal diffuser.
 10. The cooling apparatus according to claim 9, wherein the heat source is a semiconductor device, the cooling apparatus further comprising: a metal plate that is provided between the thermal diffuser and the insulating plate.
 11. The cooling apparatus according to claim 9, wherein the heat source is a semiconductor device, the cooling apparatus further comprising: a metal plate that is provided between the heat source and the thermal diffuser.
 12. A cooling apparatus for a heat source, comprising: a thermal diffuser according to claim 3, wherein the thermal diffuser includes two laminated bodies, wherein the plate surface of the thermal diffuser is one of a plurality of plate surfaces; a heat source provided to one of the plurality of plate surfaces of the thermal diffuser; an insulating plate provided to the other one of the plurality of plate surfaces of the thermal diffuser; and a cooling unit provided to a surface of the insulating plate remote from the thermal diffuser, wherein: one of the two laminated bodies of the thermal diffuser has a thickness dimension of t1; the other one of the two laminated bodies has a thickness dimension of t2; a distance, which is measured from a center position of the heat source to an end of the thermal diffuser in a longitudinal direction of the thermally-conductive plates of the one of the laminated bodies, is defined as r1; a distance, which is measured from the center position of the heat source to another end of the thermal diffuser in the longitudinal direction of the thermally-conductive plates of the other one of the laminated bodies, is defined as r2; and the dimensions t1, t2, and the distances r1, r2 satisfy the following equation: 0.5≦(t1/t2)/(r1/r2)≦2.
 13. A method of manufacturing a thermal diffuser, the method comprising: forming a laminated body by laminating a plurality of thermally-conductive plates, each of which has a plate shape, in a plate-thickness direction of the plate shape, wherein each of the plurality of thermally-conductive plates has a thermal conductivity in a plane direction of the plate shape better than a thermal conductivity in the plate-thickness direction; and forming a plate member by cutting the laminated body in a lamination direction, in which the thermally-conductive plates are laminated, along one sides of the thermally-conductive plates such that the plate member has a plate shape, wherein the plate member is formed such that one sides of the thermally-conductive plate form a plate surface that extends in the lamination direction, wherein a direction perpendicular to the plate surface corresponds to a thickness direction of the plate member.
 14. A method for manufacturing a thermal diffuser, the method comprising: forming a laminated body by laminating a plurality of thermally-conductive plates, each of which has a plate shape, in a plate-thickness direction of the plate shape, wherein each of the plurality of thermally-conductive plates has a thermal conductivity in a plane direction of the plate shape better than a thermal conductivity in the plate-thickness direction; forming a primary plate member by cutting the laminated body in the lamination direction along one sides of the thermally-conductive plates such that the primary plate member has a plate shape, wherein the primary plate member is formed such that the one sides of the thermally-conductive plates form a plate surface that extends in a lamination direction, in which the plurality of thermally-conductive plates is laminated, wherein a direction perpendicular to the plate surface corresponds to a thickness direction of the primary plate member; forming a secondary plate member by cutting off four corners of the primary plate member such that the secondary plate member has a rectangular shape, wherein a direction, in which the one sides of the thermally-conductive plates extend, is angled relative to each side of the secondary plate member, wherein the forming of the secondary plate member includes forming a plurality of secondary plate members; and arranging the plurality of secondary plate members in a direction, in which the plate surface extends, wherein a part of the plate surface of each of the plurality of secondary plate members is included in a connecting region that is connected with a heat source, wherein each of the plurality of secondary plate members has an outer peripheral section that forms an outer periphery of an entirety of the plurality of secondary plate members, wherein any point within the connecting region and any point on the outer peripheral section of each of the plurality of secondary plate members define an imaginary line therebetween, wherein a direction of the one sides of the thermally-conductive plates of each of the plurality of secondary plate members is parallel to the imaginary line. 